THE NERVOUS SYSTEM. (U3 



Lesions of the optic tbalamua do not of themselves produce entire 

 loss of sensation. If such a symptom follows, it is due to pressure upon, 

 or injury to, the posterior limb of the internal capsule. The optic 

 thalamus is connected with visual sensations and may be a reflex-centre 

 for some of the higher reflex actions. 



The optic thalamus is so closely connected with a large area of the 

 cortex that it undoubtedly must have some function in connection with 

 the mechanical or muscular movements and of expression. It is prob- 

 able that it is the organ to which automatic activities are relegated in 

 states of partial consciousness. The automatic walking, writing, speak- 



Fig. 387. Cerebellum in section and fourth ventricle, with the neighboring parts. 1, 

 Median groove of fourth ventricle, ending below in the calamus scriptorius, with the longitu- 

 dinal eminences formed by the fasciculi teretes, one on each side ; 2, the same groove, at the 

 place where the white streaks of the auditory nerve emerge from it to cross the floor of the ven- 

 tricle; 3, inferior crus or peduncle of the cerebellum, formed by the restiform body; 4, posterior 

 pyramid ; above this is the calamus scriptorius ; 5, superior crus of cerebellum, or processus o 

 cerebello ad cerebrum (or ad testes) ; 6, 6, fillet to the side of the crura cerebri; 7, 7, lateral 

 grooves of the crura cerebri ; 8, corpora quadrigemina. (From Sappey after Hirschf eld and 

 LeveillS.) 



ing, and emotional expressions, for example, that are done by men in 

 hypnotic states or in sleep, are very probably largely under the control 

 of the optic thalamus in connection with the cerebellum and associated 

 .ganglia. 



Of the functions of the external capsule and of the claustrum nothing 

 definite is known. 



The Cerebellum. 



The cerebellum (7, 8, 9, 10, fig. 354) is composed of an elongated 

 central portion or lobe, called the vermiform processes, and two hemi- 

 spheres. Each hemisphere is connected with its fellow, not only by 

 means of the vermiform processes, but also by a bundle of fibres called 

 the middle crus or peduncle (the latter forming the greater part of the 



